Description and History

NPL Listing History

NPL Status: Final

Proposed Date: 07/29/91

Final Date: 10/14/92

Deleted Date: 09/28/04

Location, Geography, and Geology

The Ralph Gray Trucking Company Superfund Site is in a 23-acre residential neighborhood of Westminster, Orange County, California. This neighborhood, north of the San Diego freeway (I405), is bounded by the Orange County flood control channel to the south, Goldenwest Avenue to the west, the US Navy railroad (abandoned) to the north, and Chestnut Street to the east. The area to the west of the site is residential and the other surrounding areas are used for light industrial and commercial activities. Approximately 450 people live in the neighborhood and around 5000 people live within one mile of the site. An elementary school and high school are within one-quarter mile of the site and a shopping center (Westminster Mall) is within one-half mile.

A drinking water aquifer, made up of an intermediate and a deep zone, lies under the site and flows from northeast to southwest. The deep zone begins at 80 feet below ground surface (bgs) and consists primarily of gravel. The intermediate zone is approximately 30 to 80 feet bgs and consists of clean to silty sands with occasional silty or clayey lenses. Above the drinking water aquifer at about ten feet bgs is a shallow perched zone of groundwater which flows generally from the north towards the flood control channel to the south of the residential area. A continuous, impermeable barrier of clay separates the perched zone from the drinking water aquifer. As a result, there is no vertical movement between the shallow perched zone and the intermediate or deep zones. It is likely that the limited amount of water in the perched zone is from leaking in-ground swimming pools and water and sewer pipelines, and from extensive residential irrigation. Given the sources of this water, its proximity to surface influences, and the limited quantity, this groundwater is not considered a potential drinking water source.

Site History

During the 1930's the immediate area was primarily used for agricultural purposes and the site was the Murdy Dairy Farm. Public records indicate that, beginning in 1936, Ralph Gray collected acid sludge, oil field wastes, and oil refinery wastes and disposed of them in four unlined pits at the farm. Due to complaints from local residents regarding the odor from the facility, the city of Westminster ordered Ralph Gray to cease operations in the late 1930s. The disposal pits were abandoned in place and remained undisturbed until the construction of 75 homes in the late 1950's. The Hintz Development Company moved the hazardous substances from the pits and buried it in two unlined trenches cut through the backyard areas of about 25 of the lots before the homes were built. The waste trenches were approximately 16 feet deep, 20 feet wide, and covered with three to four feet of soil. In addition, five homes were built directly over one of the original waste pits.

By 1965, some residents reported problems with a black sludge seeping into their yards from the ground. The sludge retained a semi-solid form at the ground surface, but became more fluid in hot weather. In addition, the seep material had a distinct and unpleasant odor. Some residents also found buried waste material in their backyards during excavation for swimming pools and house additions. As a result, the residents routinely complained to city officials about the waste throughout the 1970's.

Contaminants and Risks

Contaminated Media

Groundwater

Soil and Sludges

In general, the hazardous substances in soils at the site were found in two different forms, surface seep material and buried waste. The seep material was a black tar-like material that became fluid at 80 degrees F. The material was very pliable and had a distinct, unpleasant smell and a pH of 1.8 to 2.1. The buried waste was a black, brittle, dense material that became fluid at 180 degrees F. and had a pH as low as 0.75. Both forms of the material were comprised of volatile organic compounds (VOCs), various sulfur and organic sulfur compounds, and polynuclear aromatic hydrocarbons (PAHs).

EPA has also found that the distinctive odor associated with the waste material and adjacent soils is caused by the chemical tetrahydrothiophene and associated breakdown materials. Tetrahydrothiophene is a stenching agent used in the natural gas industry to impart a strong, noxious odor, similar to that of sewer gas, for the purpose of providing a warning in the event of a gas leak. Tetrahydrothiophene is useful for this purpose because its characteristic odor is apparent to most people at a level (1 ppb in air) below exposure levels which are associated with transient health effects such as eye or respiratory tract irritation.

Who is Involved

Investigation and Cleanup Activities

This site was addressed primarily through a "removal" action -- a project to excavate surface waste seeps and buried wastes that required demolishing and restoring some yards and structures. The State and EPA also conducted extensive studies of both soil and groundwater to ensure that the project adequately addressed any threat to human health and the environment.

Site Studies

Soils: In 1983, Orange County referred the site to the California Department of Health Services (DHS) for investigation. A DHS inspector collected samples of the waste from the interior walls of a swimming pool and determined that the seeping waste material had a pH of 1.0. In September 1987, DHS conducted soil vapor sampling at 20 sample locations to identify the types of volatile contaminants that might be present and the extent of their possible release. The samples were analyzed for four groups of compounds: halogenated organics, aromatics, aliphatics, and hydrogen sulfide. The results of the sampling indicated the residents were not endangered due to soil vapors. Neither sulfur dioxide or hydrogen sulfide were detected.

Between 1988 and 1991, DHS also completed a Multipathway Health Risk Assessment, developed a draft feasibility study (RI/FS) and prepared a draft Remedial Action Plan (RAP). The Multipathway Health Risk Assessment identified the potential exposure pathways to be through inhalation, ingestion, and dermal contact. These studies indicated that children commonly handled the seep material as a “silly putty” material, threw waste material at each other, and used the waste as a chewing gum. Adult residents reported skin discoloration and a burning sensation after handling the material during routine yard excavations. EPA also identified residents with asthma, allergies, and other respiratory problems as sensitive populations via inhalation exposure to seep material and exposed waste material. EPA was very concerned regarding the exposure of children via all pathways and incorporated the recommendations made in these documents into related EPA studies for the site.

The risk assessment concluded that the excess individual lifetime cancer risks from the contamination at the site was sufficient to warrant an EPA response action, given the close proximity of humans to the waste and the uncertainty associated with risk calculations. In addition, a June 1993 review by DHS identified the potential for an acute health threat to individuals who inhaled the emissions from disturbed seep or buried wastes.

In 1988, EPA collected further soil samples to support DHS in their investigation. Initially the agencies believed the site was not eligible for listing on the NPL due to the low likelihood that the waste material would enter the groundwater or air. However, EPA's Preliminary Assessment / Site Investigation (PA/SI) study to determine the location and extent of the waste body, completed in 1989, changed this determination. The PA/SI concluded that local residents could potentially be exposed to hazardous substances via several exposure routes, including: dermal, ingestion, and inhalation. As a result, the site was proposed for the National Priorities List (NPL) in July 1991 and the final listing was published on October 14, 1992. At the State of California’s request, EPA assumed lead responsibility for the site in January 1992. From November 1992 through April 1993, EPA conducted a focused investigation on 21 properties drilled additional 47 borings to further study the waste body.

In March 1992, EPA’s Region 9 Emergency Response Section conducted a test excavation of the waste as part of a removal assessment of the subsurface waste and contaminated soil. Results of the test excavation confirmed the presence of hazardous substances at the site and concluded that excavation could safely and successfully remove the waste body from the site. EPA completed the Engineering Evaluation and Cost Analysis (EE/CA) for this removal in August 1993. The EE/CA confirmed that the seep material would continue to migrate into yards and that residents would continue to uncover waste during construction of decks, house additions, and in-ground swimming pools, and during routine landscaping. The EE/CA found that releases of VOCs and sulfur dioxide from both seep and buried waste material had occurred and would continue to occur unless a removal action was conducted. The VOCs in the seep and buried waste material included known and potential human carcinogens and the levels of sulfur dioxide could impact individuals with impaired respiratory systems.

Site Studies

Groundwater: Orange County Water District analyzed the local, deep-aquifer groundwater in 1986 and found no indication of heavy metals, volatile organic compounds (VOCs) or other contaminants in the aquifer. During this sampling event, trichloroethene was found in levels below the MCL in two wells located two miles upgradient of the site. The location of the contamination indicated that the presence of trichloroethene in the deep aquifer was not related to the Ralph Gray Trucking Company site.

To date, nine monitoring wells have been constructed on-site, three in each of the aquifers, deep, intermediate, and shallow or perched. EPA has sampled these wells several times between 1987 and 1999 and once sampled three off-site drinking water wells. Testing indicated no contamination in the intermediate or deep aquifers or in the off-site wells. Levels of sulphur compounds found in the perched aquifer indicate that the shallow groundwater may have an unpleasant odor or taste but would not pose a significant health risk for human consumption.

The final round of sampling in late 1999 showed none of the known or probable human carcinogens found in the soils and no other chemicals typically associated with petroleum fuels. Testing did indicate certain tentatively identified compounds (TICs), notably tetrahydrothiophene and derivatives thereof, probably present as breakdown products of tetrahydrothiophene itself. As noted above, tetrahydrothiophene is a useful warning agent for propane or natural gas leaks because its noxious odor is apparent below exposure levels which are associated with transient irritant effects. Three other uncommon organic TICs were reported but little toxicity data on these compounds is available. In the one case where a drinking water guideline was available, 2-Methyl-2-propanol (CAS# 75-65-0), the highest reported level of 110 ug/l is well below the guideline of 550 ug/l established by the state of Michigan.

Summary: There is no current human exposure to the residual contamination present in the perched zone and none can be reasonably expected in the foreseeable future. In the unlikely event of future human consumption of the water from the perched zone, there is no indication from the 1999 sampling data of the presence of site-related petroleum compounds known or likely to pose a significant health risk.

Initial Actions

Between 1987 and 1991, DHS conducted annual seep removals and issued an advisory to the residents recommending they not eat vegetables and fruit grown in their yards.

EPA entered into an Interagency Agreement with the U.S. Bureau of Reclamation (USBR) to conduct the removal activities at the site. USBR conducted engineering surveys of all of the properties at the site, extensive soil sampling throughout the neighborhood to determine the extent of the waste body, prepared the removal design package, solicited bids and selected Rust Engineering as the removal contractor, solicited bids and selected a restoration contractor, and administered the temporary relocation program. The restoration contactor, Ray Gray Construction, had no business or familial relationship to Ralph Gray.

Cleanup Ongoing

The initial action memorandum for the site, dated March 29, 1994 authorized a non-time-critical removal action for the site. This decision document outlined EPA's plan to excavate contaminated soil and subsurface hazardous substances from 25-30 properties, and dispose of the contaminated materials and soil off-site at an authorized disposal facility. The removal action required the razing and restoration of backyard improvements such as house additions, swimming pools, decks, landscaping, and other structures. A subsequent action memo required the razing and reconstruction of several houses built directly above waste deposits. The removal procedures directed the heavy equipment operators to remove the visible material and to then excavate at least five additional feet into the clean, native soil. When the removal of the visible waste and overexcavation of the native soil was complete, soil samples were taken at the edge of the excavation to determine if additional excavation was necessary to complete the removal work in that area. None of the soil samples from the native soils at the edge of the excavation indicated the presence of the waste contaminants and the excavations were backfilled with clean, imported fill. The imported fill was sampled at the source as a requirement of the selection contract, and each load was sampled prior to placement at the site. The results of all of the sampling confirmed that the source and all of the backfill material were clean. After the excavation work, EPA restored affected yards and structures and provided cash settlements to homeowners whose houses were razed to allow them to rebuild or replace their homes.

Cleanup Complete

In April 2000, EPA decided to conduct soil sampling near the monitoring well that had shown the most contamination of perched groundwater to identify any potential, remaining sources. Of the fifty-one borings, only one contained a nodule of the waste material. Despite thorough sampling in the area, no additional waste material was found, and there was no evidence that the waste body had moved vertically or horizontally.
Soils extracted during the sampling had the distinctive odor noted during the earlier removal activities at the site and the compound was found to be tetrahydrothiophene and associated breakdown products. Air monitoring conducted during the sampling did not detect harmful levels of hydrogen sulfide or organic vapors in the breathing zone.

Based on the sampling results from the multiple rounds of groundwater sampling conducted at the site throughout the project, EPA has determined that neither the intermediate or deep aquifers, which are the only viable potential sources of drinking water in the area, were impacted by the activities at the site. Sampling of the perched zone in 1999 indicated that minor water quality impacts from the site were still present. However, EPA did not propose any further action because (1) this perched zone is not a viable potential source of drinking water, hence human exposure to the residual contamination is unlikely, and (2) the residual contamination therein is not considered to pose a significant health risk even in the unlikely event of human consumption.

EPA believes that it has found and removed all significant sources of hazardous waste from the site. However, deeper soils excavation (e.g. swimming pool construction) may occasionally unearth isolated nodules of waste material. EPA does not believe that any transient contact with remaining waste nodules will produce any health effects other than the potential for irritation from direct contact.

Cleanup Complete

EPA determined that the cleanup of contamination was completed and proposed to delete the Site from the NPL in July 2004. The deletion was finalized on September 28, 2004.

The site is located in a culturally diverse neighborhood; 14 different languages are spoken in the 75-home subdivision. Most site fact sheets and many other site documents are available in Spanish, Vietnamese, and English. An extensive community relations program was initiated early in the project. Community outreach has been conducted in Vietnamese, Cantonese, Portuguese, and Spanish as well as English. Community support for the project is strong. The U.S. Bureau of Reclamation provided project design and contract oversight through an inter-agency agreement with EPA.

Cleanup Results to Date

Air-borne contamination and air emissions were reduced by removing surface seeps and exposed waste on a regular basis, and by covering some areas with vapor barriers and clean soil. During the removal action, 45,000 cubic yards of hazardous substances were removed from the site, as well as landscaping and built improvements. All restoration work was completed in January 1997.